Technical Field
Embodiments of the disclosure relate to a solid-state image sensor and an image reading apparatus.
Related Art
The known solid-state image sensors, having an image reading function, have been used for imaging apparatuses such as multifunction peripherals and scanners. Such sensors include a pixel circuit for photoelectric conversion and peripheral circuits thereof including a driving circuit and a signal processing circuit. The solid-state image sensor has a column configuration with the plurality of circuits mentioned above. With this configuration, the plurality of pixel circuits and the peripheral circuits can be integrated using complementary metal oxide semiconductor (CMOS) processing technology.
Signals output form the solid-state image sensor include solid-state noise due to characteristics of the pixel circuit. To reduce the solid-state noise, the solid-state image sensor usually has a cadmium sulfide (CDS) circuit.
Using only the CDS circuit in an analog area, however, may not be enough to reduce the solid-state noise. In place of such a solid-state image sensor using the CDS circuit in the analog area, a solid-state image sensor that calculates, in a digital area, a difference between a signal level and a reset level output from a pixel block to remove the solid-state noise is known.